1. Field of the invention
The present invention relates to a tap for a gas or liquid gas cylinder, particularly of a vehicle, such as a trailer, and more particularly concerns such a tap preventing uncontrolled spillage of the cylinder contents in case the tap body is sheared-off externally of the cylinder leaving a portion of a tap root end within a cylinder aperture.
2. State of the Art
When a tap is attached to a gas or fluid cylinder its root end portion is at least partly threadably engaged in a tap aperture of the gas or liquid cylinder. One portion of the tap body is thus received within the cylinder tap aperture whereas another body portion of the tap extends from the cylinder tap aperture to the exterior of the cylinder. In case of an accident lateral or axial external forces may be applied to the portion of the tap body extending from the cylinder tap aperture, which forces may be of sufficient magnitude to cause shearing-off of the tap body approximately at the location where it extends out from the cylinder tap aperture. If the tap is sheared-off the main portion of the tap body provided with a primary valve for opening or closing a fluid flow passage through the tap is separated from a portion of the tap body that remains engaged within the cylinder tap aperture. Thus, in case of loss of the primary valve the contents of the cylinder may flow out, which is dangerous particularly if the cylinder contains toxic, inflammable or explosive gases or fluids. In the prior art it has been proposed to provide the tap upstream of the primary valve (i.e. between the primary valve and the cylinder interior) with an auxiliary check valve that is urged into closed position by a biasing spring and also by the pressure of the fluid contained in the cylinder. In the prior art this known check valve is arranged either externally of the cylinder or close to the primary valve so that it risks to be sheared-off together with the tap body portion containing the primary valve, or at least to be damaged by the external forces to such an extent that it is no longer capable to tightly close the cylinder aperture.
Check valves are also known which are spring biased to open position and closed only by the pressure in the cylinder in case of failure of the primary valve actuating mechanism.